Download File ap notes chapter 53

Chapter 53: Community Ecology
Community
Assemblage of populations of different species living close
enough for potential interaction
Interspecific interactions
Relationship of an organism with other species in its community
Types:
Competition
Predation
Herbivory
Symbiosis
Parasitism
Mutualism
Commensalism
disease
Interspecific interactions are -/-.
 Competitive exclusion: when 2 species compete for a
resource that is in short supply it can lead to the
elimination of one of those species
Ecological niche
 sum total of species’ use of biotic & abiotic resources
in its environment
 Fundamental niche



Realized niche



Theoretical resource use
ideal conditions
actual resources use
real conditions of competition & predation included
**2 species cannot coexist with identical niches
Evidence of competition in nature
 Resource partitioning


Character displacement


Sympatric species consume slightly different resources such
as food
Tendency for traits to be more divergent in sympatric
populations than in allopatric populations of the same 2
species
Parasitism (+/-)

Predator lives on or in host but seldom kills host



Parasitoidism (+/-)



Endoparasite examples: tapeworm, flukes
Ectoparasite examples: European cuckoos laying eggs in nest of
another species
Parasite kills host
Example: wasp lays eggs in host, larva hatch, feed, &
eventually kill host
Disease (+/-)

Pathogen=microscopic parasite that causes lethal harm

Symbiosis: close association between host & symbiont

Commensalism (+/0)




Mutualism (+/+)



Symbiont benefits from host while host is uneffected
Few absolute examples
Cattle egret feeds on insects that grazing cattle flush out of grass
Interaction benefits both species
Examples: nitrogen-fixing bacteria on legumes, cellulose digesting
microorganisms in digestive tracts of termites & cows, specific nectar
pollinating insects of specific flowers
Coevolution


Change in one species acts as a selective force on another
species
Counter-adaptations of the second species in turn affects
selection in the first species

Predation & Herbivory (+/-)


Predator eats its prey
Adaptations for stalking prey:

Acute senses


Heat sensors, chemical sensors, sharp eyesight
Structures

Claws, teeth, fangs, stingers, poisons
Speed & agility
 camouflage


Prey/Plant defenses include

Structural


Thorns, spines
Chemical

Toxic or bitter taste

Passive hiding



Cryptic coloration
 Shape of animal, deceptive markings (i.e. fake eyes)
Aposematic coloration
 Bright coloration as a warning of toxicity
Mimicry
 Batesian- edible species resembles inedible species
 Mullerian- two inedible species resemble each other
 Use by predator to lure prey- example… snapping turtle wags
tongue like a worm to attract fish


**Community structure is dependant on
species diversity & trophic structure; is also
effected greatly by certain species in the
community
Species diversity


The variety of different organisms that make up the
community
Components

Species richness


Total number of different species in the community
Relative abundance

Proportion of each species in the community

Trophic structure

Food chains


Food webs


Feeding relationships between organisms in the
community
Linked food chains
Limits to food chain length

Energetic hypothesis


Food chain is limited by inefficiency of energy transfer along the
chain (only 10% passed on to next trophic level)
Dynamic stability hypothesis



Long food chains are less stable than shorter food chains
a result of the magnification of population fluctuations at higher
trophic levels (top predators more likely to go extinct)
Variable environments=shorter food chains

Species with a large impact on community
structure

Dominant species


Keystone species


Species in the community with the most biomass or
abundance
Species that play a pivotal ecological role or niche
Foundation species
Species that causes physical changes in the environment
that affects the structure of the community
 Ex. beavers


Non-equilibrium model



Communities are constantly changing
Disturbance influences species diversity & composition
Disturbance
event that changes a community through removal of
organisms &/or altering resource availability
 Examples: storm, fire, drought, human activity*
*largest/widespread agent of change


Intermediate disturbance hypothesis



Moderate levels of disturbance can create conditions that
encourage species diversity by opening up new niches
low levels of disturbance lower diversity because species are
out-competed
high levels of disturbance reduce diversity because of stress
to species
Ecological succession
 Disturbed area is colonized by a variety of
species which are replaced by other species
which are again replaced….

Primary succession
Lifeless area without soil begins being inhabited by
variety of species
 Dominant species are often autotrophic prokaryotes,
lichens, & mosses to start replaced by grasses, shrubs,
& trees


Secondary succession
Existing community is cleared by a disturbance that
leaves the soil intact
 Ex. Species inhabiting a forest after a fire


Biogeographic features affect community
biodiversity

Geographic location
Species diversity is higher at equatorial region compared
to seasonally disturbed higher latitudes
 Evapotranspiration rate is higher at equatorial regions


Size

Larger geographic areas have a greater number of
species as long as all other factors are equal
Models for community organization
 Bottom-up model



Suggests alteration of biomass at lower trophic
levels will influence the higher trophic levels
Ex. Adding nutrients to soil increases plants, then
herbivores then carnivores
Top-down model/trophic cascade model


Postulates that predation controls community
organization
Ex. Removing lake predator increases herbivores
which decreases plants which increases nutrients
Hypothesis for community structure
 Interactive hypothesis


Community is an assemblage of closely linked species having
mandatory biotic interactions that cause the community to
function as an integral unit
Individual hypothesis



Community is a chance assemblage of species found in an
area because of similar abiotic requirements
Generally accepted by plant ecologists
Models for individual hypothesis:

Rivet model


Most species in a community are associated tightly with others in its
community in a web of life
Redundancy model


Web of life is loose
Increase or decrease in one species has little effect on other species
because there are redundant species to fill voids